The invention relates to a miniaturized fluid flow switch that enables a directed deflection and discharge of a fluid sample flow that is injected into a fluid carrier flow. The inventional fluid flow switch permits to switch sample flows, and to sort particles, molecules or other substances suspended and dissolved, respectively, in a sample flow according to predetermined criteria.
In G. Blankenstein; L. Scampavia; J. Branebjerg; U. D. Larsen; J. Ruzicka: xe2x80x9cFlow Switch for Analyte Injection and Cell/Particle Sortingxe2x80x9d in Analytical Methods Instrumentation, Special Issue TAS ""96, (1996), pages 82-84, a microsystem technical device is described which comprises two separate carrier flow inputs, one sample flow input, a common flow section which receives all streams, and two outlets. In this approach, the sample flow is directed into several outlet channels via the velocity of flow relation of the two carrier flows. Therein, the velocities of the passage flow in the two carrier flows can be controlled by macroscopic jet pumps. There are, however, no means specified as to sensitively controlling the two carrier flow velocities relative to each other.
A review of the current prior art methods for producing valves, controllable throttles and pumps for the microsystem technique is given in S. Shoji; M. Esashi: xe2x80x9cMicroflow devices and systemsxe2x80x9d in J. Micromech. Microeng; 4 (1994), pages 157-171xe2x80x9d. Nearly all known devices have in common that they require moving parts such as membranes or lips to affect the fluid flow. In the case of electromagnetic or pneumatic procedures the integration of a transducer proves as additionally problematic. Moving parts have the principle disadvantage of a faster aging and a higher susceptibility to trouble. Furthermore, a few methods and devices are known, which do not need any moving parts and which can be used for setting-up pumps in Microsystems. Among these are the electrohydro-dynamic principle [A. Richter, H. Sandmaier: xe2x80x9cElectrohydrodynamic pumping and flow measurementxe2x80x9d, in Proc. IEEE-MEMS Workshop, (1991) pages 99-104], [S. F. Bart, L. S. Tavrow, M. Mehrgany, J. H. Lang: xe2x80x9cMicrofabricated Electrohydrodynamic pumpsxe2x80x9d, in Sensors Actuators (1990) A21-A23, 193-197], and the electro-osmosis [D. J. Harrison, K. Seiler, A. Manz, Z. Fan: Chemical analysis and electrophoresis systems integrated on glass and silicon chips; Digest of IEEE Solid State Sensor and Actuator Workshop; (1992), 11-113]. These approaches can, however, only very limitedly be used for setting-up a controllable throttle or a valve. Furthermore, the fluids to be pumped or regulated have to satisfy very special conditions when these methods are to be used. The most important conditions are, for example, an extremely low intrinsic conductance (in the case of the electrohydrodynamic), or an extremely high intrinsic conductance and ionic strength, respectively, (in the case of the electro-osmosis). With respect to devices operating on the principle of electro-osmosis there is the additional limitation that the functionality of the device is only ensured when capillaries of a diameter of smaller than 50 xcexcm are used.
It is an object of the present invention to provide a miniaturized fluid flow switch, which does not require any moving parts and in which there are no limiting conditions as is the case with the prior art for the fluid media used.
The object is realized by the features of the first claim. Advantageous embodiments are covered by the dependent claims.
The present invention distinguishes itself by the following technical advantages: It is predestined for the integration in microsystems; it can be controlled and operated by electrical signals; and it has no moving, and hence, parts being susceptible to interferences.
The principle of the proposed fluid flow switch resides on the variation of viscosity of a liquid in dependence on the variation of its temperature. When the fluid is heated in predetermined sections of a duct by way of an electric resistance heating, then its hydrodynamic resistance changes in response. In the case of the electro-caloric fluid control, electro-caloric throttles are used for control of a carrier fluid which is used to distribute a sample liquid to different channels. In the simplest case, the carrier flow is pumped into a channel which symmetrically branches into two channels. One section of each of these two carrier flow channels is of a reduced channel cross-section related to the remaining channel cross-section of the carrier flow, whereby the reduced channel cross-section is provided with a controllable heating device. Furthermore, the carrier flow channel sections are thermally insulated relative to the other components of the fluid flow switch. The carrier flow channels funnel into the head of a distributor chamber together with the sample channel.
The distributor chamber is designed in minor-symmetry to the sample channel. At least two outlet channels are provided at the end of the distributor chamber. The sample fluid is injected right into one of the provided outlet channels by actuating the heating device provided. The relation of the velocity of flow in the two carrier flows decides at the inlet of the distributor chamber, into which of the provided outlet channels the sample fluid is pressed.